This application is based upon Japanese Patent Application No. HEI. 3-299982 filed Aug. 29, 1991, a disclosure of which is incorporated by reference.
This invention relates to an improvement of reading zoom lens systems for use with image input apparatus such as a facsimile and a scanner.
Variable resolutions have been one of the capabilities that are increasingly required to be possessed by recent models of image input apparatus including facsimiles and scanners. Reading lens systems to be used with this class of image input apparatus are usually fixed as regards the operating magnification but, on the other hand, such reading lens systems are desirably adapted for zooming since they are required to have performance. However, zooming with conventional reading lens systems is frequently impractical since aberrations such as curvature of the field will develop in increasing amounts. Even if this is possible, the applicability has been limited to the use at magnifications around the reference design value.
To overcome this difficulty and attain a desired resolution, various methods have been adopted and three typical examples are as follows: a plurality of scanners having different resolutions are used selectively; optical systems having different resolutions are incorporated in a single scanner and used in a selective manner; or the resolution is varied by electrical signal processing. However, these methods have had their own disadvantages. The first and second methods require a plurality of scanners or optical systems to attain the necessary resolutions and, furthermore, it is impossible to attain resolutions other than those offered by the scanners or optical systems provided for the lens system. In the third method which changes the resolution electrically, resolutions other than the reference value are rendered to appear as if they were the desired resolution by performing an appropriate processing on the readout data such as interpolation or subsampling but this is either time-consuming or somewhat poor in reproducibility.